1. Field of the Invention
The invention under consideration relates to a heat-generating element with at least one PTC heating element, strip conductors lying flat on it on both sides and a frame which forms at least one frame opening for holding the at least one PTC heating element.
2. Description of the Related Art
A heat-generating element of this type is known as a part of an auxiliary heater for a motor vehicle, for example, from EP 0 350 528. Further heat-generating elements are known, for example, from DE 32 08 802, DE 30 46 995 or DE 28 04 749.
Basically, with category-defining, heat-generating elements of this type, the problem that exists is that a low transition resistance should be provided by means of good mechanical contacting between the strip conductor and the PTC element, so that a current feed to the heat-generating element is possible without substantial heating at the phase interface to the PTC element. This requirement becomes particularly relevant when the heat-generating element is to be fed with high operating voltages of roughly 500 volts or more.
In electric heating devices in this category, the strip conductor, which is usually formed by an electrically conductive metal sheet, is encapsulated by a sleeve surrounding the heat-generating element, said sleeve holding the strip conductor against the at least one PTC element with a certain pressure (according to DE 32 08 802). In this state of the art, the PTC element, with the strip conductors lying on both sides, it surrounded by a metallic sleeve, which is coated on the interior with silicone rubber so that the conductive metal sheets are held in the sleeve in an insulated manner. This arrangement alone is not sufficient for building up sufficient contact pressure to press the strip conductors against the PTC element. Accordingly, the entire layer composition is surrounded by a press plate. Consequently, the known heat-generating element is relatively sluggish, i.e., the heat generated by the PTC element is relatively poorly conducted to the exterior. The known heat-generating element accordingly has a poor degree of thermal efficiency and reacts to changing thermal conditions relatively slowly.
For heat dissipation, it is known, for example, from EP 0 350 528, to place radiator elements formed from metal sheets curved in a meandering manner on both sides of the heat-generating element. These are placed against the heat-generating element with a spring bias. Because the strip conductor is provided between the radiator element and the at least one PTC element in such a way that it moves freely, the strip conductor is held against the PTC element via the spring force. There is a problem with this configuration, however, namely that particularly when the heat-generating element is operated with high voltages, wandering leakage currents via the radiator element and/or the frame cannot be avoided. Furthermore, the current-carrying parts are exposed on the exterior of the heat-generating element, which is also questionable for safety reasons.
The heating cartridge known from DE 28 04 749, in which three heat-generating elements of this category are arranged around a cylindrical axis offset by an angle of 120°, also has the aforementioned disadvantage regarding poor heat conduction. Cylindrical circular segment pieces made of an electrically insulating material are located between the individual heat-generating elements, with each having a flow conduit cut into it for a fluid to be heated by the heating cartridge. Such a configuration is inadequate, particularly in the case of convective removal of the heat generated by the PTC element through the air. In this case, heat cannot be removed from the PTC element to the extent required.
The problem forming the basis of the invention under consideration is to specify a heat-generating element in which good contacting can be ensured between the strip conductor and the at least one PTC element. Furthermore, the invention under consideration is also to specify an electric heating device that preferably comprises the heat-generating element according to the invention, whereby the heat-generating elements are positioned accurately in this heating device. The invention under consideration should also specify a method for the manufacture of a corresponding electric heating device.
To solve the problem regarding the heat-generating element, the invention under consideration proposes to enhance a heat-generating element with at least one PTC element, strip conductors lying flat on it on both sides and a frame that forms at least one frame opening for holding the at least one PTC element and that surrounds this element by means of the formation of the frame as a part of a housing which forms a structural unit with at least one of the strip conductors as well as with a wedge element, whereby the wedge element comprises a first wedge surface that runs parallel to the strip conductor and a second wedge surface that is exposed on the exterior of the housing and that is aligned diagonally to the first wedge surface.